Elastomeric foaming compositions have been developed for a variety of purposes. For example, the resiliency of elastomeric foamed compositions have advantages as noise and vibration dampening materials. Additionally, gaps can be filled by the expansion of the composition as it foams and eventually thermosets its shape during final cure. Additionally, foaming elastomeric compositions have been used in thermal insulation and electrical applications as well as flame resistant barrier applications. Many commercially available products are known and promoted for these purposes.
For example, U.S. Pat. No. 4,808,634 discloses a curable foaming silicone composition containing a vinyl polysiloxane, a hydride polysiloxane, a hydroxyl source selected from organic alcohol or organic alcohol in combination with water or hydroxylated organosiloxane, from 1 to about 250 ppm of platinum catalyst and a ketoximine compound effective to lower the foam density. Foam is created through the reaction of the hydride polysiloxane with the hydroxy source to liberate hydrogen gas. The platinum catalyst is necessary for cure and the ketoximine is recited as a critical element in the composition for reducing the density of the resultant foam.
U.S. Pat. No. 5,358,975 also relates to organosiloxane elastomeric foams. The '975 patent incorporates a triorganosiloxy end-blocked polydiorgano siloxane, an organohydrogen siloxane, a platinum catalyst, an a, β, ω-diol and a resinous copolymer containing siloxy vinyl groups. The combination of the specific diols and the resinous copolymer are recited as providing reduced density foams. Foaming is produced as a result of the reaction of the polyhydrogen siloxane and the alcohol which liberate hydrogen gas.
Numerous patents disclose the addition of blowing agents to effectuate foams. For example, see U.S. Pat. Nos. 6,110,982 and 5,373,027.
U.S. Pat. No. 6,207,730 B1 discloses an epoxy composition to which is added thermoplastic shell microspheres for inhibition of seepage of the epoxy through porous substrates. The microspheres may encapsulate a gas.
U.S. Pat. No. 6,277,898 B1 discloses epoxy resins useful as photocurable paints which use chemical or mechanical expansion agents to create foams.
U.S. Pat. No. 5,356,940 discloses a fine pored silicone foam which is formed by mixing a vinyl silicone, an organo-platinum catalyst, fumed silica, and water as a first part, with a second part which includes a silicone polymer having at least two double bonds per molecule, finned silica and polydimethylhydrogensiloxane. The two components are mixed and the reaction is subsequently pressurized, using air or nitrogen, so that the pressurized gas is present in the mixture in a dissolved form. Subsequently, the reaction mixture is heated and the dissolved gas is released, thereby forming a fine pored silicone foam.
U.S. Pat. No. 5,900,430 discloses silicone foaming compositions which contain an organopolysiloxane containing a specified amount of an alkenyl group and/or a hydroxyl group, an organohydrogenpolysiloxane, a compound having an active hydrogen, such as an alcohol, a platinum catalyst and an acetylenic alcohol compound. Foaming occurs during the cure process by the reaction of the compound having an active hydrogen group, i.e., an alcohol, with the organohydrogenpolysiloxane compound to release hydrogen gas.
U.S. Pat. No. 5,246,973 discloses a foamable silicone composition that evolves neither toxic gas or hydrogen. The foamable silicone composition comprises a thermosetting liquid silicone and 0.1 to 30 parts by weight of a thermally expansible hollow plastic micro particles. The thermosetting liquid silicone is a diorganopolysiloxane component containing alkenyl groups. An organopolysiloxane that contains at least two silicon-bonded hydrogen atoms in each polymer and a platinum metal catalyst are also included. The inclusion of the hollow plastic micro particle functions as a blowing or foaming agent that causes the composition to yield the foam.
U.S. Pat. No. 5,061,736 discloses foamable silicone compositions useful as fire-resistant joint-sealing members. The compositions disclosed contain a diorganopolysiloxane, a finely divided reinforcing silica filler, a powder of a ferrite such as a divalent metallic element such as manganese, copper, nickel, from 10 to 70 parts by weight of a finely divided inorganic material, such as mica or glass powders, finely divided platinum metal, a curing agent for silicone rubbers such as a peroxide or condensation catalyst, and the blowing agent is a composition which produces a foaming gas when exposed to elevated temperature, such as nitrogen, carbon dioxide, azobisiobutyronitrile. The blowing agent is present in the range of about 1 to 10 parts by weight.
U.S. Pat. No. 6,003,274 discloses a reinforcement web for a hollow structural member having layer of expandable foam dispersed on its principal surfaces. The foam is a resin-based material containing a blowing agent.
U.S. Pat. Nos. 5,575,526 and 6,092,864 also disclose laminates which have support members or beams bonded together with a structural foam layer. A synthetic structural resin is combined with a cell-forming agent (blowing agent) and hollow microspheres to produce the structural foam layer.
U.S. Pat. No. 6,218,442 B1 discloses a corrosion-resistant foam formulation which includes one or more thermosettable synthetic resins, one or more curatives, one or more blowing agents and one or more organic titanates or zirconates. The disclosed synthetic resins include epoxies.
Notwithstanding the state of the art, there is a continued need for curable foaming compositions which do not require the addition of blowing agents for creation of the foam, but rather rely on the in situ formation of hydrogen gas which is liberated during the curing process.